Tail-anchored (TA) proteins account for 5% of all integral membrane proteins and are characterized by a single carboxyl transmembrane domain (TMD) and a cytosolic-facing N-terminus. TA proteins play essential roles in numerous cellular pathways such as membrane biogenesis, vesicular trafficking, and apoptosis. Moreover, they are implicated in many diseases including cancer, heart disease, diabetes, as well as viral infections. In contrast to most membrane proteins, TA proteins are inserted into the endoplasmic reticulum (ER) membrane through the recently discovered, post- translational insertion GET (guided entry of TA proteins) pathway. In the GET pathway, TA proteins bound to Get3 (an ATPase chaperone), are recruited to a Get1/2 receptor complex in the ER. The goals of this proposal are to determine the physiological stoichiometry and dynamics of the Get1/2 receptor required for TA protein insertion. To this end, fluorescence and EPR spectroscopy techniques will be used to determine the oligomeric state of the receptor complex. Additionally, these methodologies will also be used to monitor the structural dynamics of the Get1/2 complex in various environments. These experiments will significantly aid in elucidating the mechanism of TA protein insertion via the GET insertion pathway. Interestingly, the therapeutic relevance of the GET pathway is further supported by the recent identification of CHD5 (congenital heart disease 5) as the human ortholog of Get1. CHD5, which function was previously unknown, is abundantly expressed in human fetal heart, kidney, lungs, and liver and has been linked to the progression of congenital heart disease in Down Syndrome patients. Due to the classification of CHD5 as a component of the GET pathway and the presence of numerous cardiac TA proteins in the sarcoplasmic reticulum (SR), the second aim of this proposal is to explore the role of CHD5 in cardiac TA protein insertion into the SR/ER using RNAi technology, cellular techniques, and confocal microscopy. Altogether, these experiments will establish the potential roles that the GET pathway may play in heart development and/or disease.